A typical data center includes a set of storage devices that provide persistent storage of data on a relatively large scale. For example, it is not uncommon for a large scale data center to include hundreds or thousands of disk drives.
A data center usually includes a set of access nodes that access data held in the storage devices in response to access requests. In a database application in a data center, for example, the access nodes typically handle database access requests such as SQL requests.
A typical access node in a data center includes an internal memory for caching data obtained from the storage devices in the data center. The caches in the access nodes of a data center usually improve the data access performance of the data center by reducing the response time to access requests when the requested data is available in a cache.
It is often desirable in a data center to reduce the power consumption of its access nodes. For example, it may be desirable to switch off some access nodes to reduce power consumption in the data center. In addition, it may be desirable to switch off access nodes to reduce heat in the data center environment. For example, a reduction in heat in a data center usually increases the reliability of hardware in the data center and usually enables more density in data center hardware. Unfortunately, prior techniques for reducing the power consumption of access nodes usually cause the loss of valuable cached data in a manner that severely impacts the overall response time performance in the data center.